Rechargeables require a constant current charger as the voltage remains fairly constant over the charge/discharge cycle, unlike a lead acid car battery, where the voltage rises and the charge current reduces as charging progresses.

marvin42 is quite correct the sanyo eneloop series (other brands are available) use a different cathode/anode configuration and retains up to 80% of the original charge after a year. So they come already charged. I have a few AA and AAA size and can confirm they do retain their charge very well.

Ni-Mh batteries loose about 10% of their charge in the first day then up to 1% everyday (say 5% a week). So they retain a usable charge for a relatively short time and so aren't suitable for low power use like clocks. The eneloop technology retains the overall charge density of a Ni-Mh but introduces a much better charge retention and can be used in low power uses.